Help with Calculation
 

Hi, I have the following XLS with 3 sheets: Credits, Inventory &
Debits.

Credits sheet (Stock sold) columns:
'Product Code', 'Product' (Text field) & 'Quantity'

Inventory fields:
'Product' (Text field), 'Company', 'Supplier', 'Product Code',
'Quantity', 'Cost Price' & 'Retail Price'.

Debits Sheet (Stock bought) columns:
'Product Code', 'Product' (Text field), 'Quantity' & 'Total cost'.

New stock entered as 'Product Code', 'Product', 'Quantity' & 'Total
Cost' into the Debits sheet. I need a method (or calculation) to allow
the following:

* Search the Inventory sheet (say column F) for the 'Product Code'
* Once found (say cell F10), update the 'Quantity' cell (say G10, but
could be G1-Gxxx; bear in mind, they may already be a value there)
with the 'Quantity' amount from the Debits sheet.
* Update the 'Cost Price' (cell H10) by dividing H10 by G10
('Quantity')
* Calculate 'Retail Price' by multiplying 'Cost Price' by 1xx%.

Same principal with the Credits Sheet too, but only 'Quantity' will
need to be updated/reduced & the 'Cost Price' brought over from the
Inventory to Credits Sheet. Any help or alternatives appreciated. Is
this too complicated for a simple XLS?!